1. Field of the Invention
The present invention relates to a portable wireless terminal. More particularly, the present invention relates to a portable wireless terminal for performing visible light communication with other devices through free space.
2. Description of the Related Art
Visible light communication is based on the fact that the wireless terminal of a transmission end transmits data-modulated visible light signals to the wireless terminal of a reception end, then the wireless reception terminal demodulates data signals from the received visible light signals. In the visible light communication, the wireless transmission terminal transmits visible light signals to the wireless reception terminal. However, under an interactive communication environment, each of the transmission side and the reception terminal either transmits or receives visible light signals without any distinction between the transmitting and receiving ends. To perform visible light communication, the wireless terminal of the transmitting side must inevitably have a light source in order to generate data-modulated visible light signals. Therefore, each wireless terminal must have a light source in order to perform interactive communication through a visible light.
FIG. 1 is a block diagram illustrating a conventional visible light communication system. The visible light communication system 100 includes first and second portable wireless terminals 110 and 120 for transmitting/receiving optical signals through free space, and the respective potable wireless terminals 110 and 120 include Light Sources (LS) 112 and 122 for generating data-modulated optical signals (i.e. electrophotonic conversion of data signal into optical signal) and outputting the generated optical signals to free space, and Optical Detectors (OD) 114 and 124 for photoelectrically converting optical signals input from free space into electrical signals.
FIG. 1 illustrates a procedure of transmitting optical signals from the first portable wireless terminal 110 to the second portable wireless terminal 120. The data-modulated optical signals output from the light source 112 of the first portable wireless terminal 110 are input into the optical detector 124 of the second portable wireless terminal 120 through free space, and the optical detector 124 photoelectrically converts the optical signals into electrical signals.
However, in a visible light communication system as described above, one wireless terminal may be under conditions (e.g. power, a light source, etc.) sufficient for transmission of visible light signals whereas the other wireless terminal may be under insufficient conditions thereof. If so, it is difficult to establish interactive communication. In order to generate visible light signals, a lot of power is required. Therefore, these conditions may emerge as a big problem in terms of the portable wireless terminal featuring a limited available time.